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  1. #1
    Join Date
    Sep 2011
    Location
    Orlando, Fl
    Posts
    4

    Who should do Manual J calc?

    My question has to do with industry standard practices. The evaporator coil is leaking on my 9 year old Carrier AC. At 9 years the AC isn't real old but I have had problems with it and decided to replace the system with a 16-18 seer unit. I intend upon getting 3-4 bids for this work.

    One of the contractors gave a price for running the Manual J calc.I don't want to pay for this three times. Should I have an independent run the calcs, or can I get one of the bidding contractors to run the numbers and supply the same print out to all?

  2. #2
    Join Date
    Feb 2008
    Location
    Massachusetts
    Posts
    702
    some contractors will charge a price to do load calcs, but if you choose them they'll deduct it from quote. Some will even do it for free, but sometimes you get what you paid for.
    It is a good idea to know up front exactly what size equipment is needed so all bids will be apples to apples.

  3. #3
    Join Date
    Sep 2011
    Location
    Orlando, Fl
    Posts
    4
    Thanks. I have a related question. My house is two stories and we have some difficulty balancing the temperature on the second level. The house is well insulated but Orlando can get hot and we use AC year round. Will the Manual J calc help identify any issues with the current ductwork and design?

  4. #4
    Join Date
    Feb 2008
    Location
    Massachusetts
    Posts
    702
    A manual D is for duct calculations and sizing, that may be helpful for your situation.

  5. #5
    Join Date
    Feb 2008
    Location
    Waffleville
    Posts
    10,339
    a properly done load calculation should help determine this issue.

    if you continue to go forward with one system, a cone system will help and can help even the tempuratures between upstairs and down.

    apples to apples also includes the type of system, warranties, and efficiencies.
    If Guns Kill People, Do Pencils Misspell Words?

    http://www.youtube.com/watch?v=An2a1...eature=related

    Before we work on artificial intelligence why don't we do something about natural stupidity?

  6. #6
    Join Date
    Sep 2011
    Location
    Orlando, Fl
    Posts
    4
    Thanks for the feedback.

    Ed

  7. #7
    Join Date
    May 2009
    Posts
    520

    Cool

    Quote Originally Posted by Ed D View Post
    My question has to do with industry standard practices. The evaporator coil is leaking on my 9 year old Carrier AC. At 9 years the AC isn't real old but I have had problems with it and decided to replace the system with a 16-18 seer unit. I intend upon getting 3-4 bids for this work.

    One of the contractors gave a price for running the Manual J calc.I don't want to pay for this three times. Should I have an independent run the calcs, or can I get one of the bidding contractors to run the numbers and supply the same print out to all?
    In NC, we are required to do Manual J calcs. It takes about half a day to do them. Would you work for half a day for free?

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,323

    Thumbs up Efficiency applies to work process and equipment

    Quote Originally Posted by simplyrollin View Post
    In NC, we are required to do Manual J calcs. It takes about half a day to do them. Would you work for half a day for free?
    Work Process and type of calc need to be reviewed


    After you perform 6 calcs and use appropriate templates, whole house calcs should take < 20 minutes for house < 2,000 square feet.

    Whole house calcs and room-by-room calcs have distinctly different functions.

    A room-by-room calc can be performed in less than an hour with a little practice.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  9. #9
    Join Date
    Jul 2002
    Location
    Yuma, AZ
    Posts
    2,361
    Quote Originally Posted by beachtech View Post
    ...if you continue to go forward with one system, a cone system will help and can help even the tempuratures between upstairs and down. ...
    I almost asked what a cone system was... only to realize you meant ZONE system. and Yes, I agree.
    "I have never let my schooling interfere with my education."
    Mark Twain
    More at: http://www.quotationspage.com/subjects/education/

  10. #10
    Join Date
    Jan 2011
    Location
    Ward, Arkansas, United States
    Posts
    842
    Quote Originally Posted by lynn comstock View Post
    I almost asked what a cone system was... only to realize you meant ZONE system. and Yes, I agree.

    I was scared to ask...thought we had warped into something new.
    "Gentlemen. You can't fight in here. This is the War Room!"-Dr. Strangelove (1964)

  11. #11
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,843
    Quote Originally Posted by dan sw fl View Post
    Work Process and type of calc need to be reviewed


    After you perform 6 calcs and use appropriate templates, whole house calcs should take < 20 minutes for house < 2,000 square feet.

    Whole house calcs and room-by-room calcs have distinctly different functions.

    A room-by-room calc can be performed in less than an hour with a little practice.
    Have to agree here As far as the OP, Manual J is part of the job but to give you the info up front makes it easy on the c ontractors to follow. I have mixed feelings about charging up front for a Manual J . We do a quick whole house to put us in the ball park for estimate purposes and do a refined Manual J (room by room) when the situation warrants it. We do not supply ANY printed Manual J information until the job is signed, sealed and delivered
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  12. #12
    Join Date
    Jun 2011
    Location
    Wake Forest, NC
    Posts
    352
    A simple block load for a change out situation should not take more than 30-60 minutes, and we do those for free on any change out we quote. If there is a need to do a room-by-room or a manual D then we do charge for it as it is more labor intensive. We do deduct the cost off the job if it is awarded to us. Minor variations on block loads may occur from one contractor to another so don't be suprised if there is some minor differences. So long as the difference is not more than 5-10% of the total load then I would not worry about it too much.

    If one says, say a cooling load of 34,000 and another says 35,500, dont worry about it. If one says 34,000 and another says 42,000 then someone has something wrong and needs to check their math.
    It's not rocket-science...

    It's electromechanical thermodynamic engineering

  13. #13
    Join Date
    Jan 2001
    Location
    Pamnyra VA.
    Posts
    710
    I found using a distance meter in addition to a tape measure helps you do it faster.Tape measure for windows and doors.

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